Diaelastic modulus change of aluminium after low temperature electron irradiation

Abstract

The changes of the elastic shear moduli C44 and C'=(C11-C12)/2 have been measured after electron irradiation of aluminium at 4.5K. Aside from dislocation pinning, a diaelastic effect which is proportional to the radiation-induced defect density has been observed. From these data the diaelastic polarizabilities under an external shear strain of the radiation-induced interstitials can be extracted. The results are very similar to those of Cu. The observed polarizabilities of alpha =-23 and alpha '=-13 are unusually large (for point defects) and highly anisotropic i.e. alpha / alpha ' approximately=2. These findings can be understood quantitatively on the basis of a model calculation which takes into account the (100) split configuration of the interstitial and the effect of the highly compressed atomic arrangement within the interstitial core region on the interatomic force constants. Thermal annealing studies indicate that di-interstitials present at the end of stage I have an even higher diaelastic polarizability than single interstitials and that the diaelastic polarizability decreases strongly when the interstitials form dislocation loops.